Anatomical terms of motion

Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative to the anatomical position of the joints. Anatomists use a unified set of terms to describe most of the movements, although other, more specialized terms are necessary for describing the uniqueness of the movements such as those of the hands, feet, and eyes.

In general, motion is classified according to the anatomical plane it occurs in. Flexion and extension are examples of angular motions, in which two axes of a joint are brought closer together or moved further apart. Rotational motion may occur at other joints, for example the shoulder, and are described as internal or external. Other terms, such as elevation and depression, describe movement above or below the horizontal plane. Many anatomical terms derive from Latin terms with the same meaning.

Motions are classified after the anatomical planes they occur in,[1] although movement is more often than not a combination of different motions occurring simultaneously in several planes.[2] Motions can be split into categories relating to the nature of the joints involved:

Angular motions occur over synovial joints and causes them to either increase or decrease angles between bones.[1]

Rotational motions move a structure in a rotational motion along a longitudinal axis, such as turning the head to look to either side.[3]

Apart from this motions can also be divided into:

Linear motions (or translatory motions), which move in a line between two points. Rectilinear motion is motion in a straight line between two points, whereas curvilinear motion is motion following a curved path.[2]

Angular motions (or rotary motions) occur when an object is around another object increasing or decreasing the angle. The different parts of the object do not move the same distance. Examples include a movement of the knee, where the lower leg changes angle compared to the femur, or movements of the ankle.[2]

The prefix hyper- is sometimes added to describe movement beyond the normal limits, such as in hypermobility, hyperflexion or hyperextension. The range of motion describes the total range of motion that a joint is able to do. [5] For example, if a part of the body such as a joint is overstretched or "bent backwards" because of exaggerated extension motion, then it can be described as hyperextended. Hyperextension increases the stress on the ligaments of a joint, and is not always because of a voluntary movement. It may be a result of accidents, falls, or other causes of trauma. It may also be used in surgery, such as in temporarily dislocating joints for surgical procedures. [6] Or it may be used as a pain compliance method to force a person to take a certain action, such as allowing a police officer to take him into custody.

Flexion and extension describe movements that affect the angle between two parts of the body. These terms come from the Latin words with the same meaning.[a]

Flexion describes a bending movement that decreases the angle between a segment and its proximal segment.[9] For example, bending the elbow, or clenching a hand into a fist, are examples of flexion. When a person is sitting down, the knees are flexed. When a joint can move forward and backward, such as the neck and trunk, flexion is movement in the anterior direction.[10] When the chin is against the chest, the head is flexed, and the trunk is flexed when a person leans forward.[10] Flexion of the shoulder or hip is movement of the arm or leg forward.[11]

Extension is the opposite of flexion, describing a straightening movement that increases the angle between body parts.[12] For example, when standing up, the knees are extended. When a joint can move forward and backward, such as the neck and trunk, extension is movement in the posterior direction.[10] Extension of the hip or shoulder moves the arm or leg backward.[11]

Abduction is the motion of a structure away from the midline while adduction refer to motion towards the center of the body.[13] The centre of the body is defined as the midsagittal plane.[3] These terms come from Latin words with similar meanings, ab- being the Latin prefix indicating "away," ad- indicating "toward," and ducere meaning "to draw or pull".[b]

Abduction is a motion that pulls a structure or part away from the midline of the body. In the case of fingers and toes, it is spreading the digits apart, away from the centerline of the hand or foot. Abduction of the wrist is also called radial deviation.[13] For example, raising the arms up, such as when tightrope-walking, is an example of abduction at the shoulder.[11] When the legs are splayed at the hip, such as when doing a star jump or doing a split, the legs are abducted at the hip.[3]

Adduction is a motion that pulls a structure or part toward the midline of the body, or towards the midline of a limb. In the case of fingers and toes, it is bringing the digits together, towards the centerline of the hand or foot. Adduction of the wrist is also called ulnar deviation. Dropping the arms to the sides, and bringing the knees together, are examples of adduction.[13]

Anterograde and retrograde flow refer to movement of blood or other fluids in a normal (anterograde) or abnormal (retrograde) direction.[21]

Circumduction is a conical movement of a body part, such as a ball and socket joint or the eye. Circumduction is a combination of flexion, extension, adduction and abduction. Circumduction can be best performed at ball and socket joints, such as the hip and shoulder, but may also be performed by other parts of the body such as fingers, hands, feet, and head.[22] For example, circumduction occurs when spinning the arm when performing a serve in tennis or bowling a cricket ball. [23]

Dorsiflexion and plantar flexion refer to extension or flexion of the foot at the ankle. These terms refer to flexion in direction of the "back" of the foot, which is the upper surface of the foot when standing, and flexion in direction of the sole of the foot. These terms are used to resolve confusion, as technically extension of the joint is dorsiflexion, which could be considered counter-intuitive as the motion reduces the angle between the foot and the leg.[25]

Dorsiflexion is where the toes are brought closer to the shin. This decreases the angle between the dorsum of the foot and the leg.[26] For example, when walking on the heels the ankle is described as being in dorsiflexion.[25]

Plantar flexion or plantarflexion is the movement which decreases the angle between the sole of the foot and the back of the leg; for example, the movement when depressing a car pedal or standing on tiptoes.[25]

Palmarflexion and dorsiflexion refer to movement of the flexion (palmarflexion) or extension (dorsiflexion) of the hand at the wrist.[27] These terms refer to flexion between the hand and the body's dorsal surface, which in anatomical position is considered the back of the arm; and flexion between the hand and the body's palmar surface, which in anatomical position is considered the anterior side of the arm.[28] The direction of terms are opposite to those in the foot because of embryological rotation of the limbs in opposite directions.[10]

Pronation and supination refer most generally to assuming prone or supine positions, but often they are used in a specific sense referring to rotation of the forearm or foot so that in the standard anatomical position the palm or sole is facing anteriorly (supination) or posteriorly (pronation).[29]

Pronation at the forearm is a rotational movement where the hand and upper arm are turned inwards. Pronation of the foot is turning of the sole outwards, so that weight is borne on the medial part of the foot.[30]

Supination of the forearm occurs when the forearm or palm are rotated outwards. Supination of the foot is turning of the sole of the foot inwards, shifting weight to the lateral edge.[31]

Nutation and counternutation[d] refer to movement of the sacrum defined by the rotation of the promontory downwards and anteriorly, as with lumbar extension (nutation); or upwards and posteriorly, as with lumbar flexion (counternutation).[39]

Opposition is the movement that involves grasping of the thumb and fingers.[40]

Protraction and Retraction refer to an anterior (protraction) or posterior (retraction) movement,[41] such as of the arm at the shoulders, although these terms have been criticised as non-specific.[42]